Field
The present disclosure generally relates to door brakes, and more particularly to door brakes for rolling doors.
Discussion of the Related Art
Rollup, or rolling, doors are widely used for industrial and commercial purposes. For example, rollup doors are commonly used as cargo bay doors, self-storage unit doors, garage doors, and the like. Rollup doors often comprise a number of interconnected leaves or slats, and this group of interconnected slats may comprise a “door curtain” or “curtain.” The curtain may be mounted to an overhead shaft, and as the rollup door is opened, or rolled up, the curtain may wind in layers about the shaft.
Doors of this type are very heavy and produce considerable vibration as they open and close. Thus, rollup doors often include a brake (coupled to the shaft) to stop their descent, should they begin to fall or descend too rapidly.
Many door brakes include a cam coupled to a central hub, where the central hub is coupled, in turn, to the overhead shaft around which a rollup door may wind and unwind. The hub may comprise a plurality of metal projections that, during normal operation, do not engage a brake housing. Rather, the projections, as they rotate with the hub, are retained away from the brake housing by a plurality of pins extending from an inner (to the brake) surface of the cam. In the event that the door to which the brake is coupled falls, the pins are configured to break away from the cam, releasing the projections, such that contact is made between the projections and the brake housing. As this occurs, the hub is no longer able to rotate, and the motion of the door is halted.
However, it is not uncommon that, over the life of the brake, the pins will slowly abrade away through the vibration induced by the motion of the rollup door. As the pins are slowly worn away, the projections coupled to the hub make their way ever closer to the brake housing until contact is eventually made, bit by bit, with the brake housing. As contact is slowly made between the rotating projections and the brake housing, the projections begin to lathe or mill away that portion of the brake housing they are intended to contact in the event that a door may fall. Finally, in the event that the door in fact falls, as what remains of the pins breaks away, the projections have worn the housing away and are unable to engage, allowing the door to fall. This occurrence is of particular concern where brakes are coupled to high cycle rollup doors.
Accordingly, it is desirable to construct a brake capable of safely operating over a large number of cycles. In particular, it is desirable to construct a brake in which the pins extending from the cam do not slowly wear away.